T
- the type of elements returned by this Spliteratorpublic interface Spliterator<T>
Collection
, an IO channel, or a generator function.
A Spliterator may traverse elements individually (tryAdvance()
) or sequentially in bulk
(forEachRemaining()
).
A Spliterator may also partition off some of its elements (using
trySplit()
) as another Spliterator, to be used in
possibly-parallel operations. Operations using a Spliterator that
cannot split, or does so in a highly imbalanced or inefficient
manner, are unlikely to benefit from parallelism. Traversal
and splitting exhaust elements; each Spliterator is useful for only a single
bulk computation.
A Spliterator also reports a set of characteristics()
of its
structure, source, and elements from among ORDERED
,
DISTINCT
, SORTED
, SIZED
, NONNULL
,
IMMUTABLE
, CONCURRENT
, and SUBSIZED
. These may
be employed by Spliterator clients to control, specialize or simplify
computation. For example, a Spliterator for a Collection
would
report SIZED
, a Spliterator for a Set
would report
DISTINCT
, and a Spliterator for a SortedSet
would also
report SORTED
. Characteristics are reported as a simple unioned bit
set.
Some characteristics additionally constrain method behavior; for example if
ORDERED
, traversal methods must conform to their documented ordering.
New characteristics may be defined in the future, so implementors should not
assign meanings to unlisted values.
A Spliterator that does not report IMMUTABLE
or
CONCURRENT
is expected to have a documented policy concerning:
when the spliterator binds to the element source; and detection of
structural interference of the element source detected after binding. A
late-binding Spliterator binds to the source of elements at the
point of first traversal, first split, or first query for estimated size,
rather than at the time the Spliterator is created. A Spliterator that is
not late-binding binds to the source of elements at the point of
construction or first invocation of any method. Modifications made to the
source prior to binding are reflected when the Spliterator is traversed.
After binding a Spliterator should, on a best-effort basis, throw
ConcurrentModificationException
if structural interference is
detected. Spliterators that do this are called fail-fast. The
bulk traversal method (forEachRemaining()
) of a
Spliterator may optimize traversal and check for structural interference
after all elements have been traversed, rather than checking per-element and
failing immediately.
Spliterators can provide an estimate of the number of remaining elements
via the estimateSize()
method. Ideally, as reflected in characteristic
SIZED
, this value corresponds exactly to the number of elements
that would be encountered in a successful traversal. However, even when not
exactly known, an estimated value value may still be useful to operations
being performed on the source, such as helping to determine whether it is
preferable to split further or traverse the remaining elements sequentially.
Despite their obvious utility in parallel algorithms, spliterators are not
expected to be thread-safe; instead, implementations of parallel algorithms
using spliterators should ensure that the spliterator is only used by one
thread at a time. This is generally easy to attain via serial
thread-confinement, which often is a natural consequence of typical
parallel algorithms that work by recursive decomposition. A thread calling
trySplit()
may hand over the returned Spliterator to another thread,
which in turn may traverse or further split that Spliterator. The behaviour
of splitting and traversal is undefined if two or more threads operate
concurrently on the same spliterator. If the original thread hands a
spliterator off to another thread for processing, it is best if that handoff
occurs before any elements are consumed with tryAdvance()
, as certain guarantees (such as the accuracy of
estimateSize()
for SIZED
spliterators) are only valid before
traversal has begun.
Primitive subtype specializations of Spliterator
are provided for
int
, long
, and double
values.
The subtype default implementations of
tryAdvance(java.util.function.Consumer)
and forEachRemaining(java.util.function.Consumer)
box
primitive values to instances of their corresponding wrapper class. Such
boxing may undermine any performance advantages gained by using the primitive
specializations. To avoid boxing, the corresponding primitive-based methods
should be used. For example,
Spliterator.OfInt.tryAdvance(java.util.function.IntConsumer)
and Spliterator.OfInt.forEachRemaining(java.util.function.IntConsumer)
should be used in preference to
Spliterator.OfInt.tryAdvance(java.util.function.Consumer)
and
Spliterator.OfInt.forEachRemaining(java.util.function.Consumer)
.
Traversal of primitive values using boxing-based methods
tryAdvance()
and
forEachRemaining()
does not affect the order in which the values, transformed to boxed values,
are encountered.
Collection
Modifier and Type | Interface and Description |
---|---|
static interface |
Spliterator.OfDouble
A Spliterator specialized for
double values. |
static interface |
Spliterator.OfInt
A Spliterator specialized for
int values. |
static interface |
Spliterator.OfLong
A Spliterator specialized for
long values. |
static interface |
Spliterator.OfPrimitive<T,T_CONS,T_SPLITR extends Spliterator.OfPrimitive<T,T_CONS,T_SPLITR>>
A Spliterator specialized for primitive values.
|
Modifier and Type | Field and Description |
---|---|
static int |
CONCURRENT
Characteristic value signifying that the element source may be safely
concurrently modified (allowing additions, replacements, and/or removals)
by multiple threads without external synchronization.
|
static int |
DISTINCT
Characteristic value signifying that, for each pair of
encountered elements
x, y , !x.equals(y) . |
static int |
IMMUTABLE
Characteristic value signifying that the element source cannot be
structurally modified; that is, elements cannot be added, replaced, or
removed, so such changes cannot occur during traversal.
|
static int |
NONNULL
Characteristic value signifying that the source guarantees that
encountered elements will not be
null . |
static int |
ORDERED
Characteristic value signifying that an encounter order is defined for
elements.
|
static int |
SIZED
Characteristic value signifying that the value returned from
estimateSize() prior to traversal or splitting represents a
finite size that, in the absence of structural source modification,
represents an exact count of the number of elements that would be
encountered by a complete traversal. |
static int |
SORTED
Characteristic value signifying that encounter order follows a defined
sort order.
|
static int |
SUBSIZED
|
Modifier and Type | Method and Description |
---|---|
int |
characteristics()
Returns a set of characteristics of this Spliterator and its
elements.
|
long |
estimateSize()
Returns an estimate of the number of elements that would be
encountered by a
forEachRemaining(java.util.function.Consumer<? super T>) traversal, or returns Long.MAX_VALUE if infinite, unknown, or too expensive to compute. |
default void |
forEachRemaining(Consumer<? super T> action)
Performs the given action for each remaining element, sequentially in
the current thread, until all elements have been processed or the action
throws an exception.
|
default Comparator<? super T> |
getComparator()
|
default long |
getExactSizeIfKnown()
|
default boolean |
hasCharacteristics(int characteristics)
Returns
true if this Spliterator's characteristics() contain all of the given characteristics. |
boolean |
tryAdvance(Consumer<? super T> action)
If a remaining element exists, performs the given action on it,
returning
true ; else returns false . |
Spliterator<T> |
trySplit()
If this spliterator can be partitioned, returns a Spliterator
covering elements, that will, upon return from this method, not
be covered by this Spliterator.
|
static final int ORDERED
trySplit()
splits a strict prefix of elements, that method
tryAdvance(java.util.function.Consumer<? super T>)
steps by one element in prefix order, and that
forEachRemaining(java.util.function.Consumer<? super T>)
performs actions in encounter order.
A Collection
has an encounter order if the corresponding
Collection.iterator()
documents an order. If so, the encounter
order is the same as the documented order. Otherwise, a collection does
not have an encounter order.
static final int DISTINCT
x, y
, !x.equals(y)
. This
applies for example, to a Spliterator based on a Set
.static final int SORTED
getComparator()
returns the associated
Comparator, or null
if all elements are Comparable
and
are sorted by their natural ordering.
A Spliterator that reports SORTED
must also report
ORDERED
.
static final int SIZED
estimateSize()
prior to traversal or splitting represents a
finite size that, in the absence of structural source modification,
represents an exact count of the number of elements that would be
encountered by a complete traversal.static final int NONNULL
null
. (This applies,
for example, to most concurrent collections, queues, and maps.)static final int IMMUTABLE
IMMUTABLE
or CONCURRENT
is expected
to have a documented policy (for example throwing
ConcurrentModificationException
) concerning structural
interference detected during traversal.static final int CONCURRENT
A top-level Spliterator should not report both CONCURRENT
and
SIZED
, since the finite size, if known, may change if the source
is concurrently modified during traversal. Such a Spliterator is
inconsistent and no guarantees can be made about any computation using
that Spliterator. Sub-spliterators may report SIZED
if the
sub-split size is known and additions or removals to the source are not
reflected when traversing.
static final int SUBSIZED
trySplit()
will be both SIZED
and SUBSIZED
.
(This means that all child Spliterators, whether direct or indirect, will
be SIZED
.)
A Spliterator that does not report SIZED
as required by
SUBSIZED
is inconsistent and no guarantees can be made about any
computation using that Spliterator.
boolean tryAdvance(Consumer<? super T> action)
true
; else returns false
. If this
Spliterator is ORDERED
the action is performed on the
next element in encounter order. Exceptions thrown by the
action are relayed to the caller.action
- The actionfalse
if no remaining elements existed
upon entry to this method, else true
.NullPointerException
- if the specified action is nulldefault void forEachRemaining(Consumer<? super T> action)
ORDERED
, actions
are performed in encounter order. Exceptions thrown by the action
are relayed to the caller.action
- The actionNullPointerException
- if the specified action is nullSpliterator<T> trySplit()
If this Spliterator is ORDERED
, the returned Spliterator
must cover a strict prefix of the elements.
Unless this Spliterator covers an infinite number of elements,
repeated calls to trySplit()
must eventually return null
.
Upon non-null return:
estimateSize()
before splitting,
must, after splitting, be greater than or equal to estimateSize()
for this and the returned Spliterator; andSUBSIZED
, then estimateSize()
for this spliterator before splitting must be equal to the sum of
estimateSize()
for this and the returned Spliterator after
splitting.This method may return null
for any reason,
including emptiness, inability to split after traversal has
commenced, data structure constraints, and efficiency
considerations.
Spliterator
covering some portion of the
elements, or null
if this spliterator cannot be splitlong estimateSize()
forEachRemaining(java.util.function.Consumer<? super T>)
traversal, or returns Long.MAX_VALUE
if infinite, unknown, or too expensive to compute.
If this Spliterator is SIZED
and has not yet been partially
traversed or split, or this Spliterator is SUBSIZED
and has
not yet been partially traversed, this estimate must be an accurate
count of elements that would be encountered by a complete traversal.
Otherwise, this estimate may be arbitrarily inaccurate, but must decrease
as specified across invocations of trySplit()
.
Long.MAX_VALUE
if infinite,
unknown, or too expensive to compute.default long getExactSizeIfKnown()
-1
.int characteristics()
ORDERED
, DISTINCT
, SORTED
, SIZED
,
NONNULL
, IMMUTABLE
, CONCURRENT
,
SUBSIZED
. Repeated calls to characteristics()
on
a given spliterator, prior to or in-between calls to trySplit
,
should always return the same result.
If a Spliterator reports an inconsistent set of characteristics (either those returned from a single invocation or across multiple invocations), no guarantees can be made about any computation using this Spliterator.
default boolean hasCharacteristics(int characteristics)
true
if this Spliterator's characteristics()
contain all of the given characteristics.characteristics
- the characteristics to check fortrue
if all the specified characteristics are present,
else false
default Comparator<? super T> getComparator()
SORTED
by a Comparator
,
returns that Comparator
. If the source is SORTED
in
natural order, returns null
. Otherwise,
if the source is not SORTED
, throws IllegalStateException
.null
if the elements are sorted in the
natural order.IllegalStateException
- if the spliterator does not report
a characteristic of SORTED
.Dracula Javadoc Sample, Made with Allan Im.